This invention is concerned with the introduction of a gene coding for a thermolabile glucoamylase when expressed in the organism into which they have been cloned.
S. cerevisiae, the yeast most commonly used in fermentation, is only capable of fermenting glucose, sucrose, fructose, maltose and maltotriose. Larger sugars and starch cannot be utilized by this yeast and, therefore, they must be hydrolyzed, usually by the use of enzymes and/or heat before fermentation of these more complex substrates can proceed. U.S. Pat. No. 4,469,791 (inventors: C. A. Colson et al, issued Sept. 4, 1984) discloses the cloning of genes coding for thermostable glucoamylases in bacteria. Thermostable glucoamylases are particularly useful in the production of materials such as high fructose corn syrup.
The nearest prior art to this invention concerns the introduction of thermostable glucocamylase genes from Saccharomyces diastaticus into Saccharomyces cerevisiase. I. Yamashita and S. Fukui in Agric. Biol. Chem. 47(11), 2689-2692 (1983) employed a STA1 gene and P. Meaden et al in Gene 34, 325-334 (1985) employed a DEX1 gene.
There is a need for a thermolabile glucoamylase in yeast fermentation of complex carbohydrates in the brewing industry. The brewing industry commonly pasteurizes beer and the pasteurization step can therefore also be used to inactivate thermolabile glucoamylases which have been previously added being particularly useful in the production of light beers.
It is an object of the invention to provide a gene coding for a glucoamylase thermolabile when expressed by a microorganism into which it has been cloned.